In recent years, mobile devices, cellular telephone devices, and car navigation devices include a display device, such as of liquid crystal display elements, on which a touch panel for enabling operational input thereon is disposed. The touch panel may also be referred to as a touch screen.
Touch panels of various types have been suggested. A typical one of those that have been suggested is a resistance film type touch panel. The resistance film type touch panel is configured such that two transparent conductive films are opposed to each other with a spacer interposed therebetween, the spacer being made of an insulating material such as acrylic resin. The two transparent conductive films serve as an upper electrode and a lower electrode of the touch panel, respectively. The transparent conductive film is formed on a surface of a transparent substrate and made of a material of a high refractive index (for example, about 1.9 to about 2.1) such as indium tin oxide (ITO).
Touch panels such as of the resistance film type may cause a phenomenon called Newton's rings to occur in some cases. Newton's rings are interference fringes that are caused by interference of light in a narrow gap between the upper and lower electrodes of the touch panel. The occurrence of Newton's rings would lead to deterioration in display quality of the display device. Thus, there have been suggestions for preventing the occurrence of Newton's rings. For example, disclosed in Patent Document 1 below is a touch panel in which the laid-around electrode is made greater in thickness than the sealing material so as to curve the upper substrate, thereby preventing the occurrence of Newton's rings.